In recent years, due to the advancement of mobile communication/wireless LAN and the advancement of communication systems (such as cognitive wireless communication) in order to improve the efficiency of existing systems, necessary for coping with a plurality of communication methods and a plurality of signal frequency bands becomes higher, so that there is an increased demand for a multi-band amplifier capable of processing multi-band signals corresponding to a plurality of communication methods and a plurality of signal frequency bands, with respect to wireless communication devices.
In order to promote a wireless device so as to be able to cope with multi-band, research and development is carried out for a type of amplifier in which signals in a plurality of frequency bands are processed by a single transmitter or receiver, aiming at miniaturization, as well as for a conventional type of amplifier in which signals are processed while switching a plurality of transmitters and receivers, each processing signals in a single different signal frequency band. The former type is configured such that the filter, the mixer, the amplifier and the like which constitute the transmitter and the receiver can cope with a plurality of frequency bands. Further, the technique has been advanced from the type in which only signals in one frequency band can be concurrently processed to the type in which signals in a plurality of frequency bands can be concurrently processed.
In the aforesaid research and development, how to achieve multi-band operation of a transmission power amplifier, which is a core technique of a wireless device, becomes a key problem; with the type in which signals in a plurality of frequency bands are amplified while switching the plurality of frequency bands, signals in the plurality of frequency bands cannot be concurrently amplified. It is recognized that, in a future mobile communication system, advanced utilization of frequencies will become increasingly important, and a concurrent-type multi-band amplifier capable of concurrently amplifying signals in a plurality frequency bands will become a key technology.
As described in NPL 1, conventionally the concurrent-type multi-band amplifier began to be used when developing a low noise amplifier. Thereafter, research and development began to be focused on the concurrent-type multi-band power amplifier; up to now, there are many reports on research and development of a plural matching type and the like which achieves a plurality of impedance matching conditions in a plurality of signal frequency bands with respect to a signal transistor. For example, such reports include NPL 2, NPL 3 and the like, as literature other than patent literature. Such reports also include the PL 1, PL 2, PL 3, PL 4 and the like, as relevant patent literature.